IMDs regularly provide functions for physiological health that are of critical importance in maintaining life as well as quality of life. For example, pacemakers can emit electrical pulses to the heart of the wearer of the IMD upon detection of an abnormal heart rhythm to increase likelihood of the heart beat returning to a normal rate. As another example, an internal defibrillator can emit electrical energy to the heart of the wearer of the IMD upon detection of ventricular fibrillation, cardiac dysrhythmia or pulseless ventricular tachycardia to increase likelihood of the heart returning to a normal sinus rhythm. As another example, an internal neurostimulator can emit electrical energy to the nervous system upon detection of pain signals to increase likelihood of pain interruption. As another example, an internal deep brain stimulation device can emit electrical energy to the brain upon detection of symptoms of neurological movement disorders to increase likelihood of return to greater physiological muscle control.
Medical care providers can monitor the IMD and assess patient current and historical physiological state to predict impending events or conditions. Providers can also initiate and modify treatment plans from time to time and/or evaluate patient compliance with nutrition, exercise and general care regiments based on data recorded in the IMD. Additionally, laboratory personnel can perform IMD diagnostics to improve function efficiencies and detection of low remaining battery life.
While low remaining battery life can be detected, detection can be performed in some instances only when the patient is at a medical facility and the IMD is being monitored. Inaccessibility to device monitoring apparatus is further exacerbated because the expected life span of an IMD (e.g., based on IMD type) can differ from the actual life span due to faults in the IMD, frequency and extent of activity while implanted in the patient and the like. Because IMDs serve life-preserving functions, and surgical intervention is often required to replace IMDs, preserving life span for IMDs is of critical importance and can lead to significant cost savings and/or can improve patient satisfaction with the IMD.
Since typical lithium batteries have an increasing series resistance as the battery is increasingly depleted, during high peak current events, regulated power supplies may go out of regulation due to battery voltage drop. As such, conventional radio frequency (RF) communication-based telemetry schemes may not operate properly as the battery is drained. Further, the longevity labeling for IMDs, which is based on anticipated battery life, can be overly conservative due to margin added to preserve telemetry operation as the battery is depleted. However, overly conservative estimates of longevity can result in waste as some IMDs can continue to function long after the time period indicated via longevity labeling.